Do what you want to do! There is alway, always, something for the kids to see and do and explore!
Since my kids first visit (when they were 2 and 4), they loved Epcot the most! Still, every trip, it's our first park to go to! Likely, it was because DH and I loved it there, we were staying at the BWV that trip, so we were close (once my son's socks got wet, forget what happened, so I stayed in the park with the kids and he ran back to our room for dry socks, and he was back in less than 30 minutes, so he was sold on staying at an Epcot resort).
I'd always say for parents of very young kids, there is always something to explore and enjoy at all of the parks!
The Mexico boat ride is fun, Living With the Land is fun, the new(ish) Nemo at the Living Seas is fun, Turtle Talk with Crush is fun, it goes on and on.